The invention concerns arrangements for adjusting the depth of cut of portable circular saws and, more particularly, arrangements for saws in which depth of cut is adjusted by pivoting movement between a shoe, which supports the saw on a workpiece, and a subassembly of the saw including the saw blade and motor, and in which depth of cut is established by the extent to which the blade emerges from the shoe.
In portable circular saws depth of cut is set by controlling the extent to which a blade portion emerges from the under or gauging surface of a shoe which supports the saw on the workpiece. This implies relative movement between the shoe and a subassembly of the saw which may include a motor and transmission with an output shaft drivably carrying the blade. The two principal known forms of articulation of this relative movement are pivotal and so-called vertical. In the first the blade and motor subassembly are pivotably connected to the shoe for pivoting about an axis parallel to the axis of rotation of the saw blade. In the second, the adjusting motion of the blade and motor subassembly relative to the shoe is a straight line perpendicular to the shoe working surface.
An advantage of the vertically adjusted saw is that a constant angular relationship between the saw handle and the shoe and work is maintained at all depths of cut. See for example U.S. Pat. No. 3,292,673 Gregory. This advantage is partially offset however in shallow cutting depth settings by the distance of the handle from the cutting edge of the blade, making operator control more difficult and leaving the hand in a poor position to push the saw. And typically, a single cantilevered support is used to support the blade and motor subassembly above the shoe with a lockable straight slide or track connection between them. In use the center of gravity of the blade and motor subassembly is usually offset from the support slide, tending to put the slide in a bind so PG,3 that adjustment of depth of cut requires careful application of a counterbalancing force by the operator to effect adjusting movement. A further disadvantage of the vertical adjustment configuration is the potential instability of the saw at very shallow depths of cut because of the relative elevation of the center of gravity of the unit above the work piece, caused by the bodily separation of the entire blade and motor subassembly from the shoe.
In West German utility model patent GBM No. 1991206, Lutz has disclosed a variation on the vertical adjustment configuration which uses a pair of spaced apart vertical supports, each with a rack and pinion, and with a common pinion shaft for effecting movement. This arrangement should avoid the binding problem and facilitate precise adjustment of depth of cut, but the system is inevitably expensive and the problems of instability and control at shallow cuts remain.
In the "pivot" type of adjustment configuration the pivotable connection between blade and motor subassembly and shoe may be ahead of the motor (front pivot) or rearwardly of the motor (rear pivot). Typically the blade and motor subassembly is "braced" from the shoe on the opposite side of the motor from the pivot by an adjustable slide arrangement. Typically the shoe, the blade and motor subassembly, and the slide arrangement connecting the blade and motor subassembly to the shoe define, respectively, the three sides of a triangle--a structure which is inherently more stable and efficient than the cantilevered arrangement of the so-called vertically adjusted saw.
A desirable depth of cut adjustment system provides for convenient, easy and speedy manipulation to set the desired depth of cut. In some applications an operator may need to change depth of cut very frequently so that an apparently minor adverse characteristic of the adjustment procedure may, in the long run, make a significant difference in operating efficiency and cost. Two significant aspects of depth of cut adjustment arrangements are first, the consistency of ease of effecting relative movement between portions of the adjusting mechanism, and second, the kind and frequency of hand movements required during an adjustment procedure. In adjusting depth of cut, typically an operator holds the saw steady with one hand grasping the main operator handle while, with his other hand, he manipulates the adjustment mechanism. In the vertical adjustment system referred to above a locking knob for an adjustable slide arrangement may be carried in fixed relation to the shoe so that, potentially, the operations of releasing the slide and moving the shoe relative to the blade may be done with one (the same) hand without removing that hand from the locking knob. But in practice, due to the overhanging weight of the motor and blade subassembly and especially at shallow cuts when slide engagement is limited, the adjusting slide may bind and the second hand must be moved to the shoe, for example, grasping it so as to counteract the binding and permit sliding movement between the shoe and the blade and motor subassembly.
In the pivoted adjustment systems, support of the blade and motor subassembly is shared between the pivot connection of the subassembly to the shoe and the mating or cooperating adjustment slide components so that the potential binding problems inherent in the cantilevered vertical adjustment system are avoided. However, in the known pivoted adjustment systems, both the slide locking control (locking knob) and the main operator's handle are fixed to the blade and motor subassembly so that after unlocking the adjustment slide the operator's hand must be moved to grasp the shoe so as to swing it on its pivot relative to the motor and blade subassembly, and then moved back again for locking the adjustment slide. An example of this depth of cut adjustment arrangement, in a rear pivot configuration, is disclosed in British patent GB No. 1,024,688 which shares a common assignee with the present invention.
A second form of pivoting depth of cut adjustment is disclosed in East German Patent No. DD243,236 Forster. Here the main operator's handle is effectively part of a subassembly including the shoe. The motor and blade subassembly pivoted to the shoe includes a slide (slot) selectively engaged by a clamping arrangement (locking knob) also carried by the shoe subassembly. In adjusting Forster therefore the operator is also required to remove his hand from the clamping device--in this case to the blade and motor subassembly--in order to pivot that assembly relative to the shoe.
A common characteristic of the two pivoted adjustment systems just described is that the main operator's handle and the clamping or locking control of the adjustment mechanism are carried on the same subassembly, thus requiring an extra hand movement in making an adjustment of depth of cut.